The present invention relates to a density correction method for recording apparatus and density correction apparatus in order to adjust recording density for a scanning type recording apparatus for performing a recording operation by using a laser beam, a thermal head or an LED. This correction technology is suitably applied to, for example, an outer-drum recording apparatus for performing a recording operation by carrying out exposure to a recording medium on a recording rotational drum.
In recent years, a multi-function image forming. apparatus has been manufactured which is arranged as follows: heat energy is applied to a toner sheet incorporating a thin film to transfer a thin film in the form of an image from the toner sheet to a recording medium which is a recording medium by using a separation phenomenon. Thus, an area-changed image and/or a line image, such as characters, is formed to form a color image, and more particularly, to form a color proof (DDCP: Direct Digital Color Proof) in a printing industrial field, form a white and black image, make a plate, manufacture filters and manufacture a printed circuit board.
The conventional multi-function image forming apparatus sometimes encounters change in the substantial density (the density in a case of a density gradation system and a record area ratio rate in actual in a case of a system for recording halftone dots) of an image recorded on a recording material owing to dimension errors of each portion, difference between recording materials among lots, change in the laser output as time elapses.
Hitherto, correction is performed by changing an electric current which is supplied to a laser output apparatus for performing exposure or time for which the exposing electric current is changed to be adaptable to the situation. Thus, the undesirable change in the substantial density of the image has been prevented. The foregoing method suffers from a problem in that a circuit for delicately adjusting the electric current and a circuit for delicately adjusting electric current pulse are required. Thus, the circuit becomes too complicated.
When an amount which must be corrected becomes different according to the gradation, the correction current and correction pulse width must be determined for each pixel. Thus, there arises a problem in that excessively complicated control must be performed.
A method has been employed with which input data is corrected with software to correct the density gradation of an obtained image. The foregoing method, which is capable of correcting all the gradation without a necessity for any complicated control, cannot perform the control in a case where color shift out of maximum gradation width capable to record, such as excessively intense highlight or unsatisfactorily thin shadow, occurs.
In view of the foregoing, an object of the present invention is to provide a density correction method for a recording apparatus and a density correction apparatus, which is capable of adequately correcting the density of all the gradation without any necessity for a complicated control circuit and which permits satisfactory productivity.
To achieve the foregoing object, a density correction method for a recording apparatus which performs recording by applying energy corresponding to input data from a recording head to a recording medium according to the first aspect of the present invention comprises recording an image on the recording medium at a predetermined halftone density, measuring record density of a result of recording of the halftone density, changing the setting value of a relative speed between the recording head and the recording medium by means of raising the relative speed when the measured record density is higher than the required density and lowering the relative speed when the measured record density is lower than the required density, recording an image on the recording medium at least two halftone densities after changing the setting value of the relative speed, and updating a density conversion table for converting input data in such a manner that the record density of a result of recording substantially coincides with the predetermined density.
The foregoing density correction method is arranged such that the relative speed between the recording head and the recording medium, for example, between the rotational speed of the recording rotational drum supporting the recording medium and the speed at which the recording medium is moved, is changed. Thus, the predetermined halftone record density is adjusted, and then the density of input data is changed by the record-density changing means in accordance with a result of recording which has been recorded as at. lest two types of halftones. Thus, only a simple control circuit is required to adequately adjust the density of all the gradation. Since greatest use of the energy applied to the recording head is permitted, the productivity (the recording speed or the like) which is required when the recording apparatus is used can significantly be improved.
Preferably, according to the second aspect of the invention, the recording head is a laser recording head for outputting a laser beam, and the recording medium is a laser thermal transfer material on which an image is formed owing to irradiation with said laser beam.
The foregoing density correction method is able to set the greatest energy which is supplied to the laser recording head, the laser output from which determines the productivity. Therefore, a high speed recording can be performed.
Further, according to third aspect of the invention, the relative speed setting value is changed from the recorded halftone density in accordance with the correspondence between a record density, which has been measured, and the relative speed.
According the foregoing method, the correspondence between the record density and the relative speed is previously measured. Thus, the relative speed. which must be set can immediately be obtained from the recorded halftone density.
A density correction apparatus according to the fourth aspect of the invention using a computer programmed to perform a density correction for a recording apparatus which performs recording by applying energy corresponding to input data from a recording head to a recording medium said density correction apparatus comprises a first recorder which records a first image on the recording medium at a predetermined halftone density, a relative speed setting value changer which measures the recording density of the first image and which changes the setting value of the relative speed between said recording head and the recording medium by means of raising the relative speed when the measured record density is higher than the required density and lowering the relative speed when the measured record density is lower than the required density, a second recorder which records a second image on the recording medium at-least two halftone densities after a set value of the relative speed has been changed and input-data-density conversion table updater which updates a density conversion table for converting input data in such a manner that the recorded density of the second image substantially coincides with the predetermined density.
The foregoing density correction apparatus is arranged such that the relative speed between the recording head -and the recording medium, for example, between the rotational speed of the recording rotational drum supporting the recording medium and the speed at which the recording medium is moved, is changed by the relative speed setting value changer. Thus, the predetermined halftone record density is adjusted, and then the density of input data is changed by the record-density changing means in accordance with a result of recording which has been recorded as at lest two types of halftones. Thus, only a simple control circuit is required to adequately adjust the density of all the gradation. Since greatest use of the energy applied to the recording head is permitted, the productivity (the recording speed or the like) which is required when the recording apparatus is used can significantly be improved.
Preferably, according to the fifth aspect of the invention, the recording head is a laser recording head for outputting a laser beam, and the recording medium is a laser thermal transfer material on which an image is formed owing to irradiation with said laser beam.
The foregoing density correction apparatus is able to set the greatest energy which is supplied to the laser recording head, the laser output from which determines the productivity. Therefore, a high speed recording can be performed.
Further, according to sixth aspect of the invention, the relative speed setting value is changed from the recorded halftone density in accordance with the correspondence between a record density, which has been measured, and the relative speed.
According the foregoing apparatus, the correspondence between the record density and the relative speed is previously measured. Thus, the relative speed which must be set can immediately be obtained from the recorded halftone density.